package com.jay.base.thread.book;

import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;

/**
 * Created by caoyuan7 on 2019/8/9.
 */
public class CountTask extends RecursiveTask<Long> {
    private static final int THRESHOLD = 1000;
    private long start;
    private long end;

    public CountTask(long start,long end){
        this.start=start;
        this.end=end;
    }
    public Long compute(){
        long sum=0;
        boolean canCompute = (end-start)<THRESHOLD;
        if(canCompute){
            for(long i =start;i<end;i++){
                sum += i;
            }
        }else {
            long step = (start+end)/100;
            ArrayList<CountTask> subTasks = new ArrayList<CountTask>();
            long pos =start;
            for(int i=0;i<100;i++){
                long lastOne = pos+step;
                if(lastOne>end){
                    lastOne=end;
                }
                CountTask subTask=new CountTask(pos,lastOne);
                pos+=step+1;
                subTasks.add(subTask);
                subTask.fork();
            }
            for(CountTask t:subTasks){
                sum+=t.join();
            }
        }
        return sum;
    }
    public static void main(String args[]){
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        CountTask task = new CountTask(0,200000L);
        ForkJoinTask<Long> result = forkJoinPool.submit(task);
        try {
            long res =result.get();
            System.out.println("sum="+res);
        }catch (InterruptedException e){
            e.printStackTrace();
        }catch (ExecutionException e){
            e.printStackTrace();;
        }
    }
}
